1. Field of the Invention
The present invention relates to a grazing incidence interferometer.
2. Description of Related Art
A grazing incidence interferometer is typically known as a device for measuring a surface profile of a workpiece (see, for instance, Patent Literature 1: JP-A-2010-32342).
The grazing incidence interferometer splits light from a light source into a reference beam and a measurement beam and lets the measurement beam be obliquely incident onto a target surface. The grazing incidence interferometer synthesizes the measurement beam reflected on the target surface and the reference beam, monitors interference fringes caused by the measurement beam and the reference beam, and measures a surface profile of the target surface by a phase shift method.
In the grazing incidence interferometer as described above, the measurement beam emitted on the target surface forms an ellipse, so that the surface profile within the elliptical area can be measured. Accordingly, by mounting the workpiece on a rotary stage and continuously measuring the surface profile within the elliptical area while rotating the rotary stage, a profile of a target surface having a wider area can be measured (see, for instance, Patent Literature 2: JP-A-2008-32690).
However, when a machining mark or the like is left on the target surface of the workpiece, an amount of the reflection beam (light intensity of the reflection beam) is changed due to the machining mark depending on a direction of the incident beam. For this reason, when the workpiece is mounted on a rotary table and is continuously measured as described above, the amount of the reflection beam may be significantly changed to cause a difficulty in profile analysis of the interference fringes.